This spring we’ve been tracking the overnight migration of birds using the Chicago Tribune‘s online weather radar. (For examples of earlier posts, go here and here.) Last night’s weather radar showed migrating birds headed north, but we’re afraid more birds left our area than arrived on the southerly winds. Here’s the Midwest radar image from early Sunday night:
The green circles on this radar image are birds taking off and heading north, starting at about 9 p.m. Chicago time. Many more birds are migrating on the western (left) side of the map. There were lots of birds taking off from our neighborhood in the Chicago area.
The image shows much more migration in the Mississippi valley (on the left side of the map) than in Ohio and eastern Indiana (on the right). Looking at a map of wind patterns, we can see why:
Overnight there were strong winds from the south over the Mississippi Valley (on the left side of the map), but weak winds to the east. (Midwest regional wind map from the Chicago Tribune's weather page).
To see why the winds blew this way, we can check the Midwest weather map for early Monday morning. It shows a high pressure area centered over northeast Indiana:
The Chicago Tribune weather map from early this morning shows a high pressure area ("H") centered over northeast Indiana. Winds blow clockwise around a high pressure center, roughly paralleling the white lines of equal pressure (called "isobars").
Winds blow clockwise around a high pressure area, which is why the winds blew from the south over Illinois and states to the west and north. Winds were calm near the center of the high in eastern Indiana and Ohio. Because birds in these areas did not have southerly winds to help their journey north, they stayed where they were.
Now lets look at the radar image from near sunrise. It shows migrating birds landing as sunrise shifts from east to west across the map:
The green circles shrink as the sun rises and migrating birds come in for a landing. The image shows few birds landing in our neighborhood, near Chicago. (This Chicago Tribune radar image runs from 5:00 to 5:50 a.m. Chicago time.)
The radar image shows few birds landing in our neighborhood just west of Chicago. Lots of birds took off from here last night, but few landed here this morning. It seems last night’s migration took birds away from our neighborhood, but did not replace them with new birds from the south.
So, what does this mean for bird watching in our neighborhood? For one thing, it’s been very quiet this morning. For the past few weeks we’ve been hearing warbler songs at sunrise, but I’ve heard none so far this morning. Maybe it’s the cool weather — the temperature was only 41 degrees at 6 a.m. — but I suspect we’ve got fewer migratory birds in our neighborhood this morning.
Today we’ll keep track of the birds that visit our yard in south Oak Park, and I’ll take a walk to nearby Columbus Park on the west side of Chicago. Check back tonight for a report on what birds we find — and what birds have left our area.
Note added at 9:15 a.m. the same day: As we were getting ready for school, we heard a Rose-breasted Grosbeak singing across the alley and an Eastern Towhee singing a few backyards to the south. So, there are still a few migrants around our neighborhood. However, we still have not heard a warbler singing this morning.
Note added at 8:00 p.m. the same day: Well, we never did see or hear a warbler in our yard today — they have left our block, at least temporarily.
The first warbler I heard today was a Tennessee Warbler singing in the Harrison Street Arts District at 10:20 a.m.as I walked to Columbus Park. I identified only seven species of warbler in Columbus Park this morning, plus there were a couple of warbler-like songs I could not identify with certainty. That’s compared with the 25 warbler species we found there during the Spring Bird Count nine days ago. After school we made a quick trip to Humboldt Park in Chicago to see a rare duck (Surf Scoter) — we saw only five species of warbler there.
This could all change tomorrow. Right now there are south winds blowing up from central Illinois and Indiana, and they should keep blowing overnight. If there are birds down there that didn’t migrate last night, they could take off and arrive here this morning — or maybe they’ll pass right through to Wisconsin.
To see what happened the next day, go here.
To learn more:
You can study bird migration using radar images from WeatherUnderground (the source of the Tribune’s images) and the National Weather Service radar website.
To learn more about using weather radar to track bird movements, try the Badbirdz – Reloaded blog, which includes a primer on using weather radar to track bird migration. For deeper explanations of bird migration and radar, try the New Jersey Audubon website.